3. Water retention properties

3.1 General

The ability of unsaturated soils to attract and retain water is quantified by the determination of water retention curves, an essential characteristic. These curves are determined by subjecting a sample to a cycle of drying and rewetting, applying stages of increasing and then decreasing suction, usually using the Richards cell. At each stage, the water content is measured by cancelling the air pressure within the cell to quickly remove the sample to be weighed; the sample is then placed back in the cell to be subjected to the next suction stage, by applying another air pressure that will generate either infiltration, if lower (rewetting path), or drainage, if higher (drying path). Water retention curves are obtained by plotting water content values in a "logarithm of suction/water...